Build 1.5 Mb disk drive?

[Protek]

I've been playing with an idea of building an external 1.5 Mb disk drive for my 500. There used to be external 1.5 Mb disk drives available back in the good old days. How does it differ from the 800 kb external unit, especially controllerwise? Are there still any HD drive mechanisms on the market that support disk change? Is there schematics available for the controller?

[Piru]

I know amiga HD floppy drive managed to put 1.71MB to normal 80 track disk (11 sectors per track), but I have never heard of 1.5MB drive...

[Effy]

Piru : isn´t it 1,76 Mb Used to have a slimline hd drive long ago  :-)

[Piru]

Well, it all depends on how you calculate it.

It's 2*160*11*512 bytes, 1760 KiB, 1.71875 MiB.

However, for some weird reason PC floppy capacity is described with kilobytes/1000 megabytes, not kilobytes/1024. Using this logic, a PC HD floppy is:

2*80*9*512 bytes, 1440 KiB, 1.40625 MiB. But, if you divide by 1000 and not 1024, you get 1.44 MB.

So indeed if you use this fubared logic you get 1.76 MB. This is not the true capacity, however.

For floppy capacity it seems PC lusers would like us to use 1024 byte kilobytes and 1000 kilobyte megabytes. No thank you, I prefer some consistency here...


[EDIT]
Ok, spotted a rounding error in my original post.. Should have been 1.72MB.
[/EDIT]

[Effy]

Indeed a funny way of calculating ... thanks for the info Piru  :-D

[Thomas]

2*160*11*512

In fact it is 2*80*22*512 resp. 2*80*18*512. "High density" does not mean twice as any tracks but the same number of tracks with twice as many sectors each.

Bye,
Thomas

[Kronos]

There was atleast 1 drive released in 1991 that had 1.6MB capacity.

It did use an HD-drive and you were advised to use HD-floppies, but in
reality it was still DD.

The extra space was gained be replacing MFM with something mor
efficient.

Needless to say that it was completly incompatible with anything else.

[Effy]

Do you mean the so called DD drives in the Amiga Technologies A1200´s that were in fact retuned HD drives which were still capable of 1,5 Mb formatting  :-?

[Protek]

I read an article about AmigaExpo in a 1990 Mikrobitti magazine (iirc). In the article there were 1.5 Mb external drives from Rossmöller and some other manufacturer. The reason I've interested in this is that DD floppies are quite hard to come by nowadays and HD floppies formatted with Amiga drives aren't quite reliable based on my experiences.

[itix]

Mikronic used to sell 1.76MB internal floppy drives for Amiga. I had one in my A1200 and replaced original internal DD drive without problems.

Edit: I recall there was an external HD drive for all Amigas. It could read DD and HD floppies normally but with HD floppies it had internal buffers to slow down transfers.

[Thomas]

Kronos wrote:
The extra space was gained be replacing MFM with something mor
efficient.

You could probably pack up to 1.4 MB onto a DD floppy if you use GCR encoding instead of MFM (GCR uses five bits per nibble while MFM uses eight bits). The Amiga floppy controller is able to handle this, you don't need extra hardware. You have to write your own floppy driver, though.

Bye,
Thomas

[amigadave]

itix wrote:
Mikronic used to sell 1.76MB internal floppy drives for Amiga. I had one in my A1200 and replaced original internal DD drive without problems.

Edit: I recall there was an external HD drive for all Amigas. It could read DD and HD floppies normally but with HD floppies it had internal buffers to slow down transfers.

It has always been my understanding that Amiga HD floppy drives operated at 1/2 the speed of 880kb drives to write the 1.76mb format to a HD floppy disk.  I did not think this had anything to do with buffers slowing down the transfer of data.   Someone correct me if I am wrong.  The external HD slimline floppy drive that Dell computers made for the Amiga for a short time might not have had to slow down the drive to write the 1.76mb format, I'll have to dig mine out of storage and test it someday.

[Joshua]

It has always been my understanding that Amiga HD floppy drives operated at 1/2 the speed of 880kb drives to write the 1.76mb format to a HD floppy disk.  I did not think this had anything to do with buffers slowing down the transfer of data.   Someone correct me if I am wrong.

That's correct, it did access at half speed, which is why using high-density disks in the Amiga was so slow.  As I recall, it was because Paula (which handles the floppy disk IO) is incapable of dealing with the data at full speed.

[Thomas]

That's correct, it did access at half speed, which is why using high-density disks in the Amiga was so slow.  As I recall, it was because Paula (which handles the floppy disk IO) is incapable of dealing with the data at full speed.

Well, actually data is transferred at the same speed, not half. The disk rotates at half speed. It's the Amiga floppy DMA channel which cannot operate at different speeds. It always writes data at the same speed. So if you want twice as much data on the same disk space, you have to rotate the disk at half speed. If you want to rotate the disk at the same speed, you have to double the DMA rate which is impossible on the Amiga's architecture.

Bye,
Thomas
 

[bloodline]

So althoguh the disk is spinning at half the speed... the data rate is the same... suggesting that you would not notice any slow down... hmmm, I imagine seeking time would be increased though :-(